The invention is related to a method for optimally operating co-generation of electricity and heat in which method the district heating power range is divided to a lower range and a higher range. The invention is also related to an optimally operating district heating power plant.
The two main sectors of energy policy are power sector and heat sector. Energy sector is combining these two sectors. In the energy activities power production (electricity production) is combined with heating to a combined method by which power and electricity may be co-generated with a better efficiency in comparison with separate production. In this combination the production of electricity is given a priority to all the benefit obtained. Electricity is made cheaper than it really is at the expense of heat: as the fuel costs are divided on the basis of cause, the portion of electricity is about three times that of heat; as the investment costs are divided on the same basis, the portion of electricity is 15 times that of heat; and in the co-generation of electricity and heat only 5% of the labour costs should be allocated to heat and the rest to electricity.
Despite of this, electrical heating is still recommended in our country by brainwashing people with false information to use electricity to heating although the specific heat consumption is the largest in the EU countries and is in Finland 50% larger than in Sweden where the state today is paying a subvention to the real estate owners who abandon using electricity for heating.
In the co-generation of electricity and heat with a conventional district heating turbine, the efficiency varies between 85 and 50%. In a system properly designed the annual average is about 70%.
Earlier, the efficiency of heating in separate heating of high-rise buildings was about 90%. Unfortunately, in that kind of heating, however, the more valuable portion of the fuel, the capacity to work, is lost. The use of fuel to produce only heat was then the biggest disadvantage of the energy sector.
As far as the utilization of fuel is concerned, the best known solution until today is to use a power engine together with a heat pump in which combination fuel may be utilized in such a way that about 1.4 to 1.6 kWh heat may be obtained from one kWh fuel.
In a so called condensing power plant producing only electricity, heating capacity of the fuel is lost with the result that fuel efficiency is only about 42%.
Because the quota of district heating turbines in our country is already built with conventional applicationsxe2x80x94in view of energy policy built too farxe2x80x94(coal-fired) condensing power is the only alternative of conventional centralized power management which during the present decade is able to provide additional power as firm electricity. Other outlines of centralized power management offer solutions which could be under production in about a decade, at the earliest.
In the condensing power application and district heating activities on the basis of the use of a boiler the significance of the indigenous renewable fuel is very small due to large losses related thereto. The losses of the condensing power process are commonly known. The losses of the district heating systems are known only by a few experts. The losses of the distribution piping are about 12 to 20% and are larger than the energy price of the used fuel because the energy is produced with quite low efficiency. Conventionally, a district heating system has been a temporary phase of gathering power as a solution aiming at the production of district heating electricity, and the district heating activities in the final mode thereof are given reasons by the low cost of the heat as a by-product of the power production: only one half of the energy price of the used fuel. District heating as the activity based on the use of a boiler is limping also in regard to boiler losses. Usually, the heat is produced with only one boiler the power of which is equal to the maximum demand of district heating. The radiation loss of a boiler is constant and about 3.5% of the rated power. The demand of the district heating power varies widely in different seasons being in the warm periods of summertime only about 8% of the maximum power, and the annual average thereof is about 30%. So, the radiation loss is about 40% in summertime and about 12% as an annual average. The annual averages of the losses of the system rise to about 30%, and thereby the efficiency as a whole is often only about 70%. Moreover, the summertime loads are often run with expensive burning oil because of the bad controllability of a boiler.
In the centralized power management, the only production mode of additional firm electricity during the decade just begun is (coal-fired) condensing power, and so the additional capacity of electricity involves always, due to the use of fossil fuel, carbon dioxide emissions increasing the greenhouse effect. Besides this, thermal load is caused to the environment by the anergy of exhaust steam the produced amount of which is about double the produced unit of electricity.
U.S. Pat. No. 4,006,857 presents a method of utilizing waste heat of large power plants. The method in comparison with the present invention is considered later in this specification.
An object of the invention is to provide a district heating power plant which operates with a principle of co-generation of electricity and heat and for which: the investment costs are lower than for a conventional district heating power plant; the fuel consumption is smaller than for a conventional district heating power plant; and the methods of control are more extensive, faster and more easy to manage than for a conventional district heating power plant.
A method according to the invention for optimally operating co-generation of electricity and heat in which method the district heating power range is divided to a lower range and a higher range, and an optimally operating district heating power plant of the invention are characterized by features presented in the accompanying claims.